Difference Between Transcription and Translation

The process of transforming the information in the gene/DNA (deoxyribonucleic acid) into the structural components of cells (proteins) is gene expression. The method of gene expression includes two main processes; transcription and translation.

The process of synthesizing RNA (ribonucleic acid), particularly mRNA (messenger RNA), is transcription. The method of coding the proteins by the mRNA (obtained from the transcription) in the ribosomes is translation. 

Although both processes are integral to expressing genes, these have many differences. The key difference is the end product of the methods, i.e., mRNA is the end product of transcription, but polypeptide or protein is the end product of translation.

Differences Between Transcription and Translation

The differences between transcription and translation arise in; the purpose, products, the method involved, enzymes involved, location, factors required, etc. 

Definition

The synthesis of mRNA complementary to a strand of DNA is called transcription. The strand of DNA is known as the gene transcript. For example, a strand of DNA containing the nucleotide sequence AAA is a template for producing the complementary sequence UUU in the RNA transcript. 

Whereas translation is the process of synthesizing amino acids by using the mRNA as a template. The sequences of nucleotides in the mRNA transcript convert into amino acids. The genetic code governs the whole translation. 

A genetic code is the set of three nucleotide codons that specifies an amino acid—for example, the codon UUU codes for the amino acid phenylalanine (Phe). 

Purpose 

The purpose of transcription is to create copies of different RNA complementary to the DNA strands for the cell to utilize in its biochemical reactions. 

In contrast, the purpose of translation is to create amino acids. The amino acids are the fundamental element of protein, an essential structural and functional component of the cell.

Factors required

RNA polymerase and associated proteins (transcription factors) are the necessary factors for RNA synthesis (transcription).

Ribosomes, initiation factors, elongation factors, and release factors are required for the completion of translation.

Location

The transcription takes place in a membrane-bound cell organelle called the nucleus. The nucleus is the organelle that covers and protects the genetic material of a eukaryotic cell. The transcription of prokaryotes occurs in the cytoplasm.

Whereas the translation occurs in the intricate macromolecular machines called the ribosomes. The ribosomes comprise three to five RNA molecules and 50-90 different proteins. 

Enzymes involved

RNA polymerase is an essential enzyme that controls, regulates, and catalyzes transcription. 

In contrast, no specific enzymes are required for translation. 

Whereas the ribosome is the protein that controls, regulates, and catalyzes translation.

Template Used

The DNA acts as the template for RNA synthesis.  

But, single-stranded RNA is the template for protein synthesis. The RNA carries the genetic code for particular amino acids. 

Initiation

RNA polymerase initiates transcription by binding to the core region called the TATA box in the promoter region of the DNA. The binding unwinds the double helix structure of DNA. The binding of transcription factors and RNA polymerase also forms the transcription initiation complex, called the transcriptional bubble. The RNA polymerase then starts to unwind the DNA strand. A short RNA (less than ten nucleotides) sequence is formed before elongation, called abortive initiation.

In contrast, the activation of starting codon AUG (methionine) by binding to tRNA is required for initiation. The initiation factor (IF1, IF2, and IF3), ribosomal units (small and large), and the activated methionine form the initiation complex.

Elongation

The RNA polymerase starts adding nucleotide bases complementary to the DNA template in the RNA formed during abortive initiation. The unwinded DNA structure rewinds as the transcriptional bubble moves to the RNA chain peeled off the template DNA. 

Whereas the elongation factors control the elongation stage of translation which occurs in 3 steps:

1. Recognition; here, new aminoacyl tRNA binds to the A site of the initiation complex,
2. Peptidyl transfer; in this step, a peptide bond forms between the starting amino acid and the newly attached amino acid. 
3. Translocation; here, the ribosome shifts a codon towards the 3’ end of mRNA, which moves the anticodon of dipeptidyl tRNA from A site to P site and deacylated tRNA from P site to E site. This shift removes the deacylated tRNA from the complex.

The first step repeats instead of starting amino acid; the P site will have dipeptidyl tRNA with starting and newly added amino acids. 

Termination

The termination of RNA synthesis occurs by two mechanisms; Rho-dependent and Rho-independent.

1. Rho-dependent; here, the Rho factor of RNA polymerase recognizes the cytidine residue and separates the DNA-RNA interaction.
2. Rho-independent; here, a G-C-rich hairpin loop is formed for terminating the RNA synthesis.

In contrast, the translation termination is signaled by stop codons UAA, UAG, and UGA, which are recognized by release factors. The release factors also dissociate the complex formed during the initiation stage.

End Products

The end product of transcription is RNA; mRNA, tRNA (transfer RNA), rRNA (ribosomal RNA), and non-coding RNA (micro RNA). 

In contrast, the end product of translation is amino acids. The amino acids are arranged in chains to form polypeptides which change into proteins.  

Modifications in End Products

The transcription end product (RNA) undergoes three essential modifications to change into a functional structure. They are; 

1. 5’ capping; here, the 5’ end of newly formed RNA is capped with 7-methyl guanine.
2. Splicing; here, the splicing (binding) of exons present in the newly formed RNA occurs with the help of small nuclear RNA (snRNA). The splicing removes all the introns of the RNA.
3. 3’ tailing; about 200 adenine residue is added to the 3’ end of pre-RNA. 

Whereas many kinds of translational modification occur before the newly formed protein is usable. Some of them are;

1. Attachment of carbohydrates to form glycoproteins.
2. Addition of isoprenyl group in order to anchor the protein to any membrane.
3. Adding the prosthetic group like heme for hemoglobulin or biotin for acetyl CoA carboxylase.
4. Acylation of the amino group in eukaryotes.
5. Removal of N-formyl methionine in bacteria enzymatically.

Inhibitory Drugs

Transcription is inhibited by hydroxyquinoline (antifungal drugs) and rifampicin (antibiotics).

The translation is inhibited by anisomycin, chloramphenicol, tetracycline, streptomycin, erythromycin, puromycin, and cycloheximide. 

Method for Invitro Detection

RT-PCR (reverse transcription polymerase chain reaction), northern blotting, RNA sequencing, and in-situ hybridization are commonly used to detect the RNA (end product of transcription).

Western blotting, immunoblotting, protein sequencing, enzyme-linked assay, radio-immunoassay, and metabolic labeling are commonly used to detect proteins (end product of translation).

Summary of The Difference Between Transcription and Translation

Properties	Transcription	Translation
Definition	It is the process of the synthesis of RNA with DNA as a template.	It is the process of synthesis of amino acids with mRNA as a template.
Products	mRNA, tRNA, rRNA, and small RNA are the end products.	A long chain of amino acids (proteins) is the end product of translation.
Catalyst and Regulators	RNA polymerase regulates and catalyzes all the steps of transcription.	GTP (guanosine triphosphate) and different factors (initiation, elongation, and release) catalyze and regulate translation.
Location	It occurs in the nucleus in eukaryotes and cytoplasm in prokaryotes.	It occurs in the ribosomal subunits of both eukaryotes and prokaryotes.
Initiation	The binding of RNA polymerase initiates the transcription to the DNA strands.	The activation of the start codon (AUG-codes methionine)) and binding of the activated methionine forms the initiation complex.
Elongation	It is simply the addition of nucleotides to the short RNA chain formed at the end of abortive initiation.	It requires different factors for recognizing the new codon, forming the peptide bond, and translocating the newly formed dipeptide to a different location within the complex.
Termination	The termination occurs by two mechanisms; rho dependent and rho independent.	The release factors recognize the stop codons (UAA, UAG, and UGA) and break the complex to terminate the addition of new amino acids.
Modification	5’ capping, 3’ tailing, and splicing are some common modifications in the final products.	Some common modifications in the final products are adding prosthetic groups, acylation, and adding carbohydrates.

References and detailed reading

• Snustad, D., & Simmons, M. (2012). Principle of Genetics (6th ed., pp. 256-269, 285-293). Hoboken, NJ: Wiley.
• Watson, J., Baker, T., Bell, S., Gann, A., Levine, M., & Losick, R. (2004). Molecular Biology of the Gene (5th ed., pp. 347-460). San Francisco: Pearson Education, Inc.
• Clancy, S. & Brown, W. (2008) Translation: DNA to mRNA to Protein. Nature Education 1(1):101 https://www.nature.com/scitable/topicpage/translation-dna-to-mrna-to-protein-393/
• Ganguly, P. Transcription. Retrieved 16 August 2022, from https://www.genome.gov/genetics-glossary/Transcription